Relationship between Augmentation Index and Wall Thickening Fraction during Hypotension in an Animal Model of Myocardial Ischemia-Reperfusion and Heart Failure

Abstract

Aims: Non-invasive indices to evaluate left ventricular changes during ischemic heart failure are needed to quantify the myocardial impairment and the effectiveness of therapeutic manoeuvres. The aims of this work were to calculate the Wall Thickening Fraction (WTF) and the Augmentation Index (AIx) and to assess the relationship between WTF and AIx using data obtained from an animal model with heart failure followed by a myocardial ischemia stage and a reperfusion stage.

Methods: Nine Corriedale sheep that had been monitored for 10 minutes during a basal stage underwent 5-minute myocardial ischemia, followed by 60-minute reperfusion. Seven of them were subjected to an induced heart failure through an overdose of halothane, two of which were treated with intra-aortic counterpulsation during the reperfusion stage. The remaining two animals were monitored during their ischemia-reperfusion stage.

Results: Data obtained in the 5 animals suffering from heart failure followed by myocardial ischemia showed that: a) heart failure induction determined decrease in cardiac output, cardiac index and systolic and diastolic aortic pressure (AoP) with respect to their basal values (p<0.05), b) myocardial ischemia decreased the WTF compared with basal and induced heart failure values (p<0.05), c) during the reperfusion stage accompanied by induced heart failure, WTF increased with respect to values observed during the ischemia induction stage (p<0.05); nevertheless, basal values were not recovered after reperfusion (p<0.05). During this 60-minute stage, systolic and diastolic AoP values were lower (p<0.05) than those at the basal stage.

Conclusion: AIx and WTF values calculated from synchronically recorded values of aortic pressure and left ventricular wall thickness during the reperfusion stage in all animals (n = 9) showed a negative correlation (p<0.05). Analysed data provided evidence of a negative relationship between a left ventricular index of myocardial function and an arterial index obtained from AoP waves.

Keywords: Augmentation index; aortic counterpulsation; heart failure; hypotension.; myocardial ischemia; wall thickening fraction.